Most plant B-type cyclin genes are expressed during the M phase of the cell cycle, and the promoters of some of these genese are known to direct M phase-specific transcription. However, the minimal cis elements that control the phase-dependent activation of B-type cyclin genese have not been defined. In their analysis of the promoter of a Catharanthus roseus B-type cyclin gene, which appears on pages 331–341 of this issue, Ito et al. show that a conserved 9-bp sequence, termed the M phase-specific activator (MSA), is necessary and sufficient for M phase-specific transcription of the luciferase (luc) reporter gene. The cover, which depicts tobacco suspension culture cell transformed with a triple MSA::luc construct, illustrates this point; luc activity (visualized in red, purple, and white) is restricted to those cells that are undergoing mitosis.